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[Bug 1342053] [NEW] [Thinkpad T420s] Brightness dims when unplugging external monitor and cannot be changed afterwards

 

Public bug reported:

Steps to reproduce

1) Plug a T420s to an external monitor using Displayport
2) Both external and internal monitor look right
3) Unplug (via software or hardware) the external monitor

Expected results:
The brightness in the internal monitor stays the same and it can be changed through system keys or system settings

Actual results:
The brightness in the internal monitor dims and it cannot be changed until the system is rebooted

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: linux-image-3.13.0-30-generic 3.13.0-30.54
ProcVersionSignature: Ubuntu 3.13.0-30.54-generic 3.13.11.2
Uname: Linux 3.13.0-30-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.2
Architecture: amd64
AudioDevicesInUse:
 USER        PID ACCESS COMMAND
 /dev/snd/controlC0:  yaiza      2214 F.... pulseaudio
 /dev/snd/pcmC0D0p:   yaiza      2214 F...m pulseaudio
CurrentDesktop: Unity
Date: Tue Jul 15 11:50:50 2014
EcryptfsInUse: Yes
InstallationDate: Installed on 2014-05-05 (71 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417)
MachineType: LENOVO 4171CTO
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.13.0-30-generic.efi.signed root=UUID=62b47b3b-711a-4ea1-bae0-a59dc3eaaff1 ro quiet splash vt.handoff=7
RelatedPackageVersions:
 linux-restricted-modules-3.13.0-30-generic N/A
 linux-backports-modules-3.13.0-30-generic  N/A
 linux-firmware                             1.127.4
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 07/11/2012
dmi.bios.vendor: LENOVO
dmi.bios.version: 8CET54WW (1.34 )
dmi.board.asset.tag: Not Available
dmi.board.name: 4171CTO
dmi.board.vendor: LENOVO
dmi.board.version: Not Available
dmi.chassis.asset.tag: No Asset Information
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: Not Available
dmi.modalias: dmi:bvnLENOVO:bvr8CET54WW(1.34):bd07/11/2012:svnLENOVO:pn4171CTO:pvrThinkPadT420s:rvnLENOVO:rn4171CTO:rvrNotAvailable:cvnLENOVO:ct10:cvrNotAvailable:
dmi.product.name: 4171CTO
dmi.product.version: ThinkPad T420s
dmi.sys.vendor: LENOVO

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: Confirmed


** Tags: amd64 apport-bug trusty

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https://bugs.launchpad.net/bugs/1342053

Title:
   [Thinkpad T420s] Brightness dims when unplugging external monitor and
  cannot be changed afterwards

Status in “linux” package in Ubuntu:
  Confirmed

Bug description:
  Steps to reproduce

  1) Plug a T420s to an external monitor using Displayport
  2) Both external and internal monitor look right
  3) Unplug (via software or hardware) the external monitor

  Expected results:
  The brightness in the internal monitor stays the same and it can be changed through system keys or system settings

  Actual results:
  The brightness in the internal monitor dims and it cannot be changed until the system is rebooted

  ProblemType: Bug
  DistroRelease: Ubuntu 14.04
  Package: linux-image-3.13.0-30-generic 3.13.0-30.54
  ProcVersionSignature: Ubuntu 3.13.0-30.54-generic 3.13.11.2
  Uname: Linux 3.13.0-30-generic x86_64
  ApportVersion: 2.14.1-0ubuntu3.2
  Architecture: amd64
  AudioDevicesInUse:
   USER        PID ACCESS COMMAND
   /dev/snd/controlC0:  yaiza      2214 F.... pulseaudio
   /dev/snd/pcmC0D0p:   yaiza      2214 F...m pulseaudio
  CurrentDesktop: Unity
  Date: Tue Jul 15 11:50:50 2014
  EcryptfsInUse: Yes
  InstallationDate: Installed on 2014-05-05 (71 days ago)
  InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417)
  MachineType: LENOVO 4171CTO
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.13.0-30-generic.efi.signed root=UUID=62b47b3b-711a-4ea1-bae0-a59dc3eaaff1 ro quiet splash vt.handoff=7
  RelatedPackageVersions:
   linux-restricted-modules-3.13.0-30-generic N/A
   linux-backports-modules-3.13.0-30-generic  N/A
   linux-firmware                             1.127.4
  SourcePackage: linux
  UpgradeStatus: No upgrade log present (probably fresh install)
  dmi.bios.date: 07/11/2012
  dmi.bios.vendor: LENOVO
  dmi.bios.version: 8CET54WW (1.34 )
  dmi.board.asset.tag: Not Available
  dmi.board.name: 4171CTO
  dmi.board.vendor: LENOVO
  dmi.board.version: Not Available
  dmi.chassis.asset.tag: No Asset Information
  dmi.chassis.type: 10
  dmi.chassis.vendor: LENOVO
  dmi.chassis.version: Not Available
  dmi.modalias: dmi:bvnLENOVO:bvr8CET54WW(1.34):bd07/11/2012:svnLENOVO:pn4171CTO:pvrThinkPadT420s:rvnLENOVO:rn4171CTO:rvrNotAvailable:cvnLENOVO:ct10:cvrNotAvailable:
  dmi.product.name: 4171CTO
  dmi.product.version: ThinkPad T420s
  dmi.sys.vendor: LENOVO

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Follow ups

References